Ultra High Vacuum Flanges & Viewports that can achieve UHV performance at 10 -12cc/second established with fluorocarbon o-ring seals & a differentially pumped vacuum system. By pumping on the differential section with only a mechanical pump, UHV pressures on the inside can be routinely achieved. This is the most reliable solution to replace & eliminate vacuum seal failures made with either epoxy or solder. Diameters include 2.75”, 3.38”, 4.50” & 6.0” Visit http://www.reflexusa.com/ulhivaufl.html